This application is based on Patent Application No. 2001-24547 filed Jan. 31, 2001 in Japan the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a printing apparatus and a printing method of a so-called multi-path printing system in which the same printing area on a printing medium is repeatedly scanned by a printing head to complete an image on the printing medium.
2. Description of the Related Art
Recently, printers of various printing systems have been developed due to the spread of personal computers, word processors or facsimile receivers in offices or homes. Of them, printers of an ink jet system are most suitable for a personal use in home or the office because they have various advantages such as easy in color correspondence, low in operation noise, high in printing grade for various media or small in size.
Of them, an ink jet printing apparatus of a serial scanning type in which the printing operation is carried out while a printing head reciprocates on a printing medium has been widely spread in the market because a high grade image is obtainable at a lower cost.
To obtain a high grade printed image, it is desirable that positions, sizes and shapes of dots formed by a plurality of printing elements in a printing head are uniform. If characteristics of the dots printed by the plurality of printing elements has an irregular distribution or deviation, it appears as the irregularity of density in the obtained image.
The present applicant has proposed in Japanese Patent Application Laid-open No. 7-52390 (1995) a system in which the same printing area on a printing medium is repeatedly scanned by a printing head to complete an image while a random mask pattern is applied as a thinning pattern in the respective scan to the printing data in the same printing area.
By using a mask made by using random numbers, this system causes the periodicity in the irregularity of density to be difficult to be visually recognized, as well as prevents the printed pattern from being synchronized with the thinned-out pattern.
On the other hand, in a recent ink jet printing head, printing elements (ink ejection openings in this case) are densely arranged in a wider range (printing width) for obtaining a high quality printed image at a high speed.
When such a printing head is used, however, the number of printing elements simultaneously actuated during the printing operation increases, as a total number of the printing elements increases. While an average current value used for the printing head can be reduced by using the randomly thinned-out mask pattern described above in comparison with a case wherein an image is completed by only one printing scan, there may be a random mask having a structure in that numerous printing elements are simultaneously driven to instantaneously require a large current.
If the instantaneous current value is large, problems may occur in that the manufacturing cost increases due to a structure for reducing a resistance of a path for applying a voltage to the printing head or for reducing noises.
The present invention has been made in view of the above-mentioned problems, and an object thereof is to reduce in a multi-path printing system the number of printing elements driven simultaneously so that a current instantaneously flowing into the printing head is restricted.
In an aspect of the present invention, there is provided a printing apparatus using a printing head on which a plurality of printing elements are arranged, scanning the printing head in a direction different from the arranging direction of the plurality of printing elements relative to a printing medium, and forming an image on the same printing area on the printing medium by a plural times of the scans of the printing head, the apparatus comprising:
means for providing thinning patterns for the plural times of the scan, the thinning patterns being for determining whether or not each of the printing elements concerned with a printing operation in the same printing area is to be driven, and the thinning patterns being complementary to each other, and
means for applying the thinning patterns complementary to each other in relation to the printing elements which are simultaneously driven when the printing operation is carried out in the same printing area.
In another aspect of the present invention, there is provided a printing method using a printing head on which a plurality of printing elements are arranged, scanning the printing head in a direction different from the arranging direction of the plurality of printing elements relative to a printing medium, and forming an image on the same printing area on the printing medium by a plural times of the scans of the printing head, the method comprising the steps of:
providing thinning patterns for the plural times of the scan, the thinning patterns for determining whether or not each of the printing elements concerned with a printing operation in the same printing area is to be driven, and the thinning patterns being complementary to each other, and
applying the thinning patterns complementary to each other in relation to the printing elements which are simultaneously driven when the printing operation is carried out in the same printing area.
In the apparatus or the method according to the present invention, the thinning pattern may be a mask of a predetermined size in which data for determining whether or not the printing element is to be driven are arranged randomly.
Further, means for or a step of relatively conveying the printing medium in a direction perpendicular to the scanning direction between the scans by an amount less than the arrangement width of the plurality of printing elements may be comprised.
The printing elements concerned with the printing operation carried out in the same printing area may be used while being divided into a plurality of sections, and the applying means or step may apply the thinning patterns to the plurality of sections during each of the plural times of the scans, and may apply the thinning patterns complementary to each other to the respective sections during the plural times of the scans.
The printing head may be a head for performing printing by ejecting an ink.
Here, the printing head has heating elements or electrothermal transducers for generating thermal energy to make the ink to film-boil, as an energy for ejecting the ink.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.
Incidentally, hereafter, the wording xe2x80x9cprintxe2x80x9d (hereinafter, referred to as xe2x80x9crecordxe2x80x9d also) represents not only forming of significant information, such as characters, graphic image or the like but also represent to form image, patterns and the like on the printing medium irrespective whether it is significant or not and whether the formed image elicited to be visually perceptible or not, in broad sense, and further includes the case where the medium is processed.
The wording xe2x80x9cprinting mediumxe2x80x9d represents not only paper to typically used in the printing apparatus but also cloth, plastic film, metal plate and the like and any substance which can accept the ink in broad sense.
Furthermore, the wording xe2x80x9cinkxe2x80x9d has to be understood in broad sense similarly to the definition of xe2x80x9cprintxe2x80x9d and should include any liquid to be used for formation of images, designs, patterns and the like or for processing of the printing medium.
Still further, the wording xe2x80x9cnozzlexe2x80x9d, as far as not mentioned specifically, represents to an ejection opening, a liquid passage communicated with the opening and an element for generating an energy used for ink, in summary.